Reland PR #4040: Support Qwix quantization on NNX with cross-environment import compatibility

[RexBearIU]

Description

This PR relands the changes from PR #4040 ("Support Qwix quantization on NNX") which was previously merged and reverted.

To prevent import failures across different environments, this PR introduces a dual-compatible fallback import block for flax_util in src/maxtext/layers/quantizations.py.

Context & Why:

The original PR used from qwix._src import flax_util.
Due to a packaging layout discrepancy, different builds/distributions of the Qwix package even within the exact same version identifier (e.g., 0.1.6) present different internal path structures (some placing flax_util directly in qwix._src and others placing it under qwix._src.utils).

Using a single hardcoded path caused immediate compile/import errors depending on the specific package layout present in the target environment.

Solution:

We introduce a try-except fallback block:

# Support different packaging structures across environments even within the same Qwix version identifier (imports from _src.utils vs _src).
try:
  from qwix._src.utils import flax_util
except ImportError:
  from qwix._src import flax_util

This allows the codebase to compile and run correctly across environments with different packaging layouts of the Qwix package.

FIXES: #4040

Tests

The changes were verified by running the unit test suite in the local environment:

python3 -m pytest tests/unit/quantizations_test.py

Output: 8 passed, 16 skipped in 2.90s (0 failures).

Checklist

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• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

❌ Patch coverage is 67.56757% with 24 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/layers/nnx_wrappers.py	33.33%	10 Missing and 6 partials ⚠️
src/maxtext/layers/quantizations.py	83.33%	4 Missing and 2 partials ⚠️
src/maxtext/layers/nnx_decoders.py	50.00%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[NuojCheng]

Thank you Jacky!